The heart of a computer is a magnetic hard disk drive (HDD) which typically includes a rotating magnetic disk, a slider that has read and write heads, a suspension arm above the rotating disk and an actuator arm that swings the suspension arm to place the read and/or write heads over selected circular tracks on the rotating disk. The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent an air bearing surface (ABS) of the slider causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk. When the slider rides on the air bearing the write and read heads are employed for writing magnetic impressions to and reading magnetic signal fields from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
The volume of information processing in the information age is increasing rapidly. In particular, it is desired that HDDs be able to store more information in their limited area and volume. A technical approach to this desire is to increase the capacity by increasing the recording density of the HDD. To achieve higher recording density, further miniaturization of recording bits is effective, which in turn typically requires the design of smaller and smaller components.
The further miniaturization of the various components, however, presents its own set of challenges and obstacles. FIG. 5 schematically shows a structure of a magnetic head 500 which performs conventional thermal flying-height control (TFC), according to the prior art. A read element 502 and a write element 504 are formed in succession on a substrate 506. A heater element 508 which is activated in order to perform TFC may be placed between the substrate 506 and the read element 502, between a write coil 516 and the read element 502, between the read element 502 and the write element 504, etc. In FIG. 5, this heater element 508 is shown positioned between the read element 502 and the write element 504, but is not so limited.
During TFC, the gap or clearance 512 between the recording medium 510 and the air bearing surface (ABS) 514 of the magnetic head 500 (typically one of the write element 504 and the read element 502) is controlled by applying more or less heat from the heater element 508, such as by controlling the current, power, or energy supplied to the heater element 508, and utilizing thermal expansion of materials near the heater element 508 caused by heat produced by the heater element 508 to cause enlargement of an area of the magnetic head 500 at the ABS 514.
FIGS. 6A-6B schematically show the TFC clearance 512 during operation of a magnetic disk drive that utilizes the magnetic disk 500. During a read operation, as shown in FIG. 6A, thermal expansion takes place due to heat generated by the read element 502. It has been confirmed by experimentation and heat deformation calculations that clearance fluctuations do not occur. The clearance 512 during a read operation is controlled by causing deformation of the ABS 514 due to thermal expansion caused by the heat generation near a center (denoted by cross 602) of the heater element 508. Setting the clearance 512 during a read operation at a predetermined amount ensures stability of the recording and reproduction characteristics of the magnetic disk drive and guards against deterioration in reliability of the magnetic head 500 due to contact (“touchdown”) between the magnetic head 500 and the disk medium 510.
When the clearance 512 is set for a read operation, the clearance 512 during a write operation, as shown in FIG. 6B, may also be set to any amount according to the placement and shape of the heater element 508.
On the other hand, when the magnetic disk drive is performing a write operation, the heat generated by the write element 504 produces clearance fluctuations (referred to below as “write protrusion”) because of thermal expansion caused by heat generated near a center (denoted by cross 604) of the write element 504 (this heat is also near the coil 516). Therefore, the shape produced as a result of thermal expansion during write operations, as shown in FIG. 6B, differs from a shape produced during read operations, as shown in FIG. 6A. It is therefore useful to implement TFC to account for write protrusion that is different from read protrusion when the magnetic disk is performing write operations.
However, there is a need to record to magnetic disk media having a high coercive force because of increased recording density in typical magnetic disk media. Consequently, the current used for a write operation has increased over time and taken a higher frequency due to an increase in the write signal output. This results in the heat generated by the write element during a write operation to similarly increase, with write protrusion becoming larger. Furthermore, write protrusion varies according to specific write signals. For example, the write signal frequency is different at an inner circumference of the disk medium as compared to an outer circumference of the disk medium, with write protrusion also varying. Therefore, it would be useful to account for this variation in TFC.